The present invention relates generally to a vehicular power transmission control system equipped with an engine and an electrical motor generator to drive a vehicle and particularly to a control system that executes an automatic speed-ratio change of an automatic transmission, through which the rotational driving forces of the engine and the electrical motor generator are transmitted to drive wheels.
Recently, a vehicle equipped with a so-called hybrid-type drive source, i.e., an electrical motor generator in addition to an engine, has been developed and come into practical use. In such a hybrid vehicle, generally, the engine and the electrical motor generator are used to drive the vehicle in a most fuel-efficient way, and while the vehicle is in a deceleration, the electrical motor generator, which is driven by a driving force of the drive wheels, is used to generate electricity for charging the battery (recovering energy). As a result, such a vehicle has achieved a high fuel efficiency. However, in a case where the electrical motor generator is used for driving the drive wheels, if the charge of the battery is insufficient, the electrical motor generator cannot provide a driving torque that is necessary for driving the vehicle. To solve this problem, conventionally, the speed change ratio of the transmission is controlled to shift toward the LOW speed ratio in correspondence to the remaining charge of the battery.
Even though the charge of the battery is sufficient enough to drive the electrical motor generator, there is an occasion where the electrical motor generator cannot provide a required or predetermined output. This can happen, for example, if the temperature of the battery or the electrical motor generator becomes too low or too high to operate in good condition or if the electrical motor generator malfunctions. If the electrical motor generator experiences such a problem, for example, while the vehicle is traveling downhill, the torque driving the electrical motor generator for recovering energy (referred to as xe2x80x9crecovery torquexe2x80x9d) may become small enough to weaken the action of engine brake provided by the electrical motor generator. Another problem may be a worsening of the acceleration performance of the vehicle.
It is an object of the present invention to provide a power-transmission control system for a vehicle, which system can provide securely a predetermined engine brake or a predetermined acceleration performance even in a case where the electrical motor generator fails to perform an initial or intended performance.
To achieve this objective, the present invention provides a vehicular power-transmission control system that transmits the rotational driving forces of an engine and an electrical motor generator to drive wheels through an automatic transmission (for example, the continuously variable transmission CVT described in the following embodiment) by controlling the speed change ratio of the automatic transmission in correspondence to the operational condition of the vehicle. Additionally, the control system corrects the speed change ratio of the transmission in correspondence to the difference between the actual output of the electrical motor generator and the requested output of the electrical motor generator that is set correspondingly to the operational condition of the vehicle.
In a case where the battery is not charged sufficiently or the electrical motor generator cannot perform as expected even though the battery is charged sufficiently, the actual output of the electrical motor generator falls short of the requested output of the electrical motor generator. To solve such a problem, the vehicular power-transmission control system according to the present invention corrects the speed change ratio in correspondence to the difference between the actual output and the requested output. For example, in a case where the vehicle is traveling downhill with an engine brake being activated, if the actual output of the electrical motor generator (electrical power for recovering energy) falls short, then the force of the engine brake becomes small. To solve such a problem, the speed change ratio of the transmission is corrected (generally toward the LOW speed ratio) in correspondence to the difference between the actual output and the requested output to increase the rotational speeds of the electrical motor generator and the engine. This action results in an increase in the force of the engine brake and eliminates the insufficiency in the braking force. In another case where during an acceleration of the vehicle, if the actual output of the electrical motor generator (electrical power for acceleration) falls short, the speed change ratio is also corrected (also toward the LOW speed ratio) in correspondence to the difference between the actual output and the requested output. This action results in an increase in the driving torque, eliminating the insufficiency in the driving torque.
Preferably, the automatic transmission comprises a continuously variable transmission, and the target engine rotational speed is set in correspondence to the operational condition of the vehicle (for example, the vehicle speed and the accelerator opening), so that the speed change ratio of the continuously variable transmission is controlled to bring the rotational speed of the engine to the target engine rotational speed. In this case, the target engine rotational speed is corrected to correct the speed change ratio in correspondence to the difference between the actual output and the requested output of the electrical motor generator.
It is preferable that the vehicular power transmission control system further comprise inclination-detecting means for detecting the inclination of the road surface where the vehicle is traveling (for example, the inclination sensor described in the following embodiment) and that the speed change ratio be corrected in correspondence to the difference between the actual output of the electrical motor generator, which is being driven by a force from the wheels, and the requested output of the electrical motor generator that is set correspondingly to the current vehicle speed. By this control, any insufficiency which may occur in the output of the electrical motor generator is compensated as the correction of the speed change ratio functions to increase the rotational speeds of the electrical motor generator and the engine, generating a force to eliminate the insufficiency in the engine-braking action.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.